1. Field of the Invention
The present invention relates to mounting structures for electro-hydraulic drive units in production machines and, more particularly, to a vibration damping supporting device for the hydraulic pump of a self-contained electro-hydraulic power unit which is mounted in the machine base of an injection molding machine.
2. Description of the Prior Art
In U.S. Pat. No. 3,982,856 is disclosed a vibration damping mounting arrangement of an electro-hydraulic power unit for an injection molding machine, in which the hydraulic pump and the electric drive motor form a compact structurally rigid unit reaching horizontally through a side wall of the machine base, the inside of which forms a tank compartment containing hydraulic fluid. This power unit is so arranged that the hydraulic pump is located on the inside of the vertical supporting wall, above the hydraulic fluid, while the electric drive motor is located on the outside of the wall, for better cooling. This drive unit is supported on the vertical wall of the machine base by engaging the wall portion surrounding a large aperture with clamping flanges and interposed resiliently compressible discs of a vibration absorbing elastomeric material. A tapered centering formation in the supporting wall assures that the clamping flanges of the power unit cannot shift into metal-to-metal contact with the wall.
It has now been found that this power unit mounting arrangement, though free of rigid contact points with the supporting machine base, nevertheless may become subject to radial vibrations of the hydraulic pump which are not attenuated by the straddle-type mount of the power unit on the side wall of the machine base. These radial vibrations, in turn, have a tendency to generate secondary vibrations. For example, a considerable noise output by the coupling elements of the power unit has been traced to these radial vibrations.
While efforts have been made in the past to develop special low-noise hydraulic pumps of various types, including radial piston pumps, axial piston pumps, and rotating vane pumps, the actual noise reducing benefits of these efforts have been modest at best.